Modeling the behavior of sand-fines mixtures using a critical state model

A review of the current literature on soil behavior modeling reveals the great success of constitutive models proposed within the critical state soil mechanics framework. Imam et al. (2005) proposed a critical state constitutive model for predicting the behavior of sand consolidated to a wide range of void ratios and pressures. The model uses capped yield surfaces and was formulated with special emphasis on its ability to simulate the behavior of loose liquefiable sand. Since sands with fines are abundant in nature, it is often necessary to modify existing models proposed for clean sand to enable them to predict the behavior of sand-fines mixtures. In recent years, the equivalent granular void ratio has been used as an alternative state variable in order to obtain a single trend of variation for some aspects of behavior of sand-fines mixtures such as the critical state condition. In this paper, application of this concept for upgrading the mentioned constitutive model in order to enable it to simulate the behavior of such mixtures is attempted. It is shown that the approach implemented in the current study successfully takes into account effects of non-plastic fines on the sand-fines mixture behavior, and that the modified model simulations are in good agreement with the observed behavior of such mixtures. Performances of two relationships proposed for the determination of the equivalent granular void ratio used in the modified model are also compared. •The equivalent granular void ratio concept is used to upgrade the model of Imam et al. (2005) for sand-fines mixtures.•Four series of undrained monotonic triaxial tests are used for validation of the upgraded model.•The modified model simulations are in good agreement with the experimental results.•Results obtained from two equations proposed previously for the equivalent granular void ratio are also compared.